Ema, small boards found hanging at many shrines and some temples are votive plaques, but someone, I think it was Ian Reader, called them "postcards to the gods", and that made a lot of sense to me.
The most common shape for ema is 5-sided, kind of house shaped, but there are also other shapes including spoon shaped and others with cutouts.
The most common design nowadays are the 12 animals of the oriental zodiac, the animal of each year being common, but bigger shrines will often have designs that reflect something about thye history or the kami of the specific shrine.
The top photo is from Dojoji Temple in Wakayama, famous for a story about a maiden that was a very popular kabuki play. The second photo is from a small shrine in Wakayama City, Shiogama Shrine. Why the ema are vertical rectangles I dont know. The 3rd photo, a monkey carrying a gohei, is commonly found at shrines to Sarutahiko, but the regular monkey pictures below it are a standard year of the monkey ema. The final photo shows a collection of diverse ema hanging at Ubusuna Shrine in the grounds of Kokawadera Temple.